/*
 * Copyright 2002-2017 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.beans.factory.config;

import java.util.Properties;
import java.util.prefs.BackingStoreException;
import java.util.prefs.Preferences;

import org.springframework.beans.factory.BeanDefinitionStoreException;
import org.springframework.beans.factory.InitializingBean;
import org.springframework.lang.Nullable;

/**
 * Subclass of PropertyPlaceholderConfigurer that supports JDK 1.4's
 * Preferences API ({@code java.util.prefs}).
 *
 * <p>Tries to resolve placeholders as keys first in the user preferences,
 * then in the system preferences, then in this configurer's properties.
 * Thus, behaves like PropertyPlaceholderConfigurer if no corresponding
 * preferences defined.
 *
 * <p>Supports custom paths for the system and user preferences trees. Also
 * supports custom paths specified in placeholders ("myPath/myPlaceholderKey").
 * Uses the respective root node if not specified.
 *
 * @author Juergen Hoeller
 * @see #setSystemTreePath
 * @see #setUserTreePath
 * @see java.util.prefs.Preferences
 * @since 16.02.2004
 */
public class PreferencesPlaceholderConfigurer extends PropertyPlaceholderConfigurer implements InitializingBean {

    @Nullable
    private String systemTreePath;

    @Nullable
    private String userTreePath;

    private Preferences systemPrefs = Preferences.systemRoot();

    private Preferences userPrefs = Preferences.userRoot();


    /**
     * Set the path in the system preferences tree to use for resolving
     * placeholders. Default is the root node.
     */
    public void setSystemTreePath(String systemTreePath) {
        this.systemTreePath = systemTreePath;
    }

    /**
     * Set the path in the system preferences tree to use for resolving
     * placeholders. Default is the root node.
     */
    public void setUserTreePath(String userTreePath) {
        this.userTreePath = userTreePath;
    }


    /**
     * This implementation eagerly fetches the Preferences instances
     * for the required system and user tree nodes.
     */
    @Override
    public void afterPropertiesSet() {
        if (this.systemTreePath != null) {
            this.systemPrefs = this.systemPrefs.node(this.systemTreePath);
        }
        if (this.userTreePath != null) {
            this.userPrefs = this.userPrefs.node(this.userTreePath);
        }
    }

    /**
     * This implementation tries to resolve placeholders as keys first
     * in the user preferences, then in the system preferences, then in
     * the passed-in properties.
     */
    @Override
    protected String resolvePlaceholder(String placeholder, Properties props) {
        String path = null;
        String key = placeholder;
        int endOfPath = placeholder.lastIndexOf('/');
        if (endOfPath != -1) {
            path = placeholder.substring(0, endOfPath);
            key = placeholder.substring(endOfPath + 1);
        }
        String value = resolvePlaceholder(path, key, this.userPrefs);
        if (value == null) {
            value = resolvePlaceholder(path, key, this.systemPrefs);
            if (value == null) {
                value = props.getProperty(placeholder);
            }
        }
        return value;
    }

    /**
     * Resolve the given path and key against the given Preferences.
     *
     * @param path        the preferences path (placeholder part before '/')
     * @param key         the preferences key (placeholder part after '/')
     * @param preferences the Preferences to resolve against
     * @return the value for the placeholder, or {@code null} if none found
     */
    @Nullable
    protected String resolvePlaceholder(@Nullable String path, String key, Preferences preferences) {
        if (path != null) {
            // Do not create the node if it does not exist...
            try {
                if (preferences.nodeExists(path)) {
                    return preferences.node(path).get(key, null);
                } else {
                    return null;
                }
            } catch (BackingStoreException ex) {
                throw new BeanDefinitionStoreException("Cannot access specified node path [" + path + "]", ex);
            }
        } else {
            return preferences.get(key, null);
        }
    }

}
